I have a 89 XJ Limited 4.0 And I need a new engine (Bad Rear Main, and a lot of blow by) I’d rather replace the engine than tear it down to replace the rear main plus it has 170K. Anyways I can get a rebuilt reman. Long block for 1024 with a 70/7 year warrantee or I can get a complete long block with all acc. for like 500 out of a 96 Grand Cherokee.

The question is how hard would it be to get this to work. The engine mounts the same to the frame, and tranny I assume? I know the 96 motor is a OBDII but I'm talking about using the stock 89 computer, are the sensor harnesses for example the throttle body and other sensors going to be the same, if not are they sliceable? Will this work and has anyone heard of such a thing? Any advice would be greatly appreciated

The two are not compatible at all! The '89 injection system was made by Renix and went out of production with the '91 models. Nothing from the '89 will "talk" to the 96 parts/sensors. You could install everything related to the injection system from the '89 engine onto the '96 though.

Bolt the entire intake to the newer head. Same thing with your existing exhaust manifold. If you want to use the newer exhaust and it's not the same as the old, then yes your exhaust will have to be modified.